One project will not open

I have two libraries: "completed" and "to work on."

Everything is fine except one project in the (ironically) Completed library will not open. There is a "loading" window that is only half visible and never goes away. FCP seems from that point frozen.

I have restarted, rebuilt the directory with disk warrior, but nothing works. Only this single project does not open.

Any ideas how to fix this much appreciated.

Waddo